The semiconductor industry is very dependent upon sources of ultrahigh purity reagents. Other industries also have high purity requirements, but few compare with the purity requirements in the semiconductor industry. Vapor delivery systems are used in a number of manufacturing processes. For example, vapor delivery systems are used in the manufacture of optical wave guides. Such systems are described in U.S. Pat. Nos. 3,826,560; 4,235,829; and 4,276,243, the disclosure of which is incorporated herein by reference. Thin films are sometimes produced by vapor delivery system technology, see HANDBOOK OF THIN FILM TECHNOLOGY, Maissel and Glang, McGraw-Hill, New York, 1970. Film deposition techniques are generally described, as applicable to the semiconductor industry, in ENCYCLOPEDIA OF SEMICONDUCTOR TECHNOLOGY, Grayson (Ed) John Wiley, New York, 1984.
With particular application to the manufacture of semiconductors, it is known to provide semiconductor devices by reacting a silicon wafer, appropriately prepared with the semiconductor component pattern thereon, with the vapor from liquid source materials or dopants. Among these liquid source materials are boron tribromide, phosphorous oxychloride, phosphorous tribromide, silicon tetrabromide, arsenic trichloride, arsenic tribromide, antimony pentachloride and various combinations of these.
Traditionally, in this industry, these dopants were provided in ampules, typically made of quartz with a stem which can be broken off. The ampule was shipped from the manufacturer of the dopant to the semiconductor producer. The ampule was broken and the material transferred to a bubbler. An inert gas, typically was bubbled through the reagent, partially or fully saturating the gas with the reagent, and then the reagent laden inert gas was fed under controlled conditions into a silicon wafer furnace. All of this, of course, is well-known and somewhat old technology at this point in time. A great step forward was made in this technology with the development by Dr. John C. Schumacher and Dr. Andre' Lagendijk of a bubbler which was suitable for both shipment and use in the process line. This type of bubbler is described in U.S. Pat. Nos. 4,134,514 and 4,298,037. In using bubblers of this type, it was only necessary to purge the conduit lines after the bubbler had been connected, and then open the bubbler. This greatly reduced the amount of contamination and provided a much higher quality product and a more consistent product with a lower reject rate. While this was a great advance in the technology, there yet remains the problem of changing the bubbler. These processes are typically carried out in a clean room, in which access is limited and special clothing is required. Even under the best conditions, the entry of operating personnel into the clean room disrupts the equilibrium which exists there during production. This results from the introduction of different temperature and composition atmosphere from outside the clean room, and simply from the presence of an operator. Each individual introduces with his clothing and with his person certain impurities into the atmosphere. These and other factors tend to reduce the quality of the product, and increase the rejection rate each time an operator has to enter the clean room.
In addition, the physical handling of bubblers filled with these reagents, which tend to be highly poisonous and very reactive, presents a certain safety problem. While with adequate care and suitable safety precautions the processes are carried out with a very high degree of safety, there is some risk always present.
The present invention is designed to reduce the risk and to significantly increase the time between entry of an operator into the clean room and, thereby, improve the efficiency of the process and reduce the reject rate, as well as improve the quality of the product. These and other objects are accomplished by providing a system which eliminates the need to replace the bubbler, or to manually refill it. The bubbler is automatically maintained between a minimum and a maximum level. All of this is accomplished from a refill reservoir using unique and significant process steps and apparatus to prevent contamination and to assure safety. Thus, it is one of the facets of this invention to provide a system for automatically refilling bubblers, or the like, which are used as vapor delivery systems.